Process of constructing bituminous macadam roads



Patented July 3, 1934 UNITED STATES PATENT OFFICE PROCESS OFCONSTRUCTING BITUMINOUS MACADAM ROADS No Drawing. Application February10, 1932, Serial No. 592,194

3 Claims.

This invention relates to the process of constructing roads by means ofwood tar and has for its object to render the process more expeditious,cheaper, and safer.

5 In the construction of roads and highways of the bituminous macadamtype a base several inches thick of lime rock or oyster shells or acombination of both, is prepared and thoroughly rolled. This base isallowed to season and consolidate and becomes a solid monolith throughthe action of the materials entering into its construction. It is,however, susceptible to the action of water and has a soft Wearingsurface.

The present practice is to place a priming coat of coal tar over thebase, then a layer of petroleum asphalt and finally a covering ofcrushed granite in order to exclude water and provide a hard Wearingsurface. It is essential that the asphalt top and the base be firmlybound together and it has been found from experience that petroleumproducts are not satisfactory for the purpose.

I have found that the use of a priming coat of wood tar sometimes calledpitch of wood or its derivative wood tar oil, or a priming coat composedof wood tar or wood tar oil and petroleum products in the constructionof a road of the bituminous macadam type, as a binder between the baseand the asphalt top coat produces a road which is very durable and suchpriming coat binds the asphalt top coat to the base of the road in asatisfactory and relatively permanent manner. Such priming coatpenetrates the base much deeper than a petroleum priming coat andadheres 5 more firmly to the asphalt top coat. It can be applied whenthe base is wet, is not corrosive or injurious to the workman andbecause of the rapidity of the penetration, permits the road to be usedmore quickly. If a combination of wood tar or wood tar oil and petroleumproducts is used, the proportions can be varied to suit the constructionof the base and the materials used in the base and the top coat. As anexample I have found that a mixture of sixty parts of wood tar or woodtar oil and forty parts of petroleum fuel oil of high specific gravitymakes an excellent priming coat over a lime rock base.

I claim:

1. A macadam road construction comprising essentially a base aggregatewhich is predominantly alkaline in character and an asphalt wearingsurface, and an intermediate priming layer comprising one of the groupconsisting of wood tar and wood tar oil, said intermediate layer beinghighly penetrative of said base aggregative and distinctly acid inreaction, whereby secure adhesion between said base aggregate and thesaid intermediate priming layer, as well as between the latter and saidwearing surface, is assured.

2. The construction defined in claim 1, wherein said base aggregateconsists essentially of one of the group comprising lime rock, oystershells, and an admixture of lime rock and oyster shells.

3. The construction set forth in claim 1, wherein said priming layerconsists of a mixture of about sixty parts of a wood tar constituent andabout forty parts of petroleum fuel oil of high specific gravity.

RAYMOND B. HARRIS.

